1. Field of the Invention
The present invention relates to magnetic tape transport systems, and more particularly to tape transport systems in which magnetic tape is bidirectionally transferred between a pair of reels while maintaining a substantially linear acceleration of the tape loops in associated buffer columns during tape acceleration and deceleration intervals and with a control response independent of the tape diameter on the reels.
2. Description of the Prior Art
Magnetic tape transport systems in which high tape speeds occur intermittently and bidirectionally require servo controls to enable the tape to rapidly accelerate and decelerate to and from a desired running speed without data loss or distortion resulting from variations in tape speed caused by non-linear system frequency response, or errors in the sensed position or velocity of the tape from which the various servo control signals are derived. Systems of the prior art, particularly single capstan tape transports, generally require longer than optimum buffer columns for the tape since the system response is incapable of responding quickly enough to use such short length buffer columns. Other problems, such as erroneous tape speed and position servo control signals are caused by variation in the reel tape pack radius, dependence upon potentially inaccurate position or velocity information from more than a minimum of loop sensors, a lack of continuous tape loop position information, and limit cycling or oscillation of the tape in the buffer columns are all problems of systems of the prior art which are overcome by the present invention.
The tape transport system described by U.S. Pat. No. 3,304,018, wherein the tape loop acceleration is a function of the tape pack radius, is nonlinear, and employs longer than optimum buffer columns is illustrative of the prior art. Additionally, by biasing the tape position sensors, the referenced patent further increases the required buffer length.
Another tape transport system of the prior art is described by U.S. Pat. No. 3,713,606 in which velocity information is digitally quantized, resulting in limit cycling of the tape loops in the buffer columns and high power use. In the present invention, tape loop acceleration is independent of reel size, with loop acceleration being linear, thereby enabling the use of optimally short buffer columns without limit cycling and with the tape loop stablized at the point of maximum displacement in the buffer columns.
U.S. Pat. No. 3,454,960 is illustrative of another tape transport system of the prior art in which a large number of loop sensors are employed.
Another system of the prior art is described by U.S. Pat. No. 3,319,901 in which the tape reel servo motor is controlled by summing signals representative of tape speed, direction and position, with the position signals being derived from a plurality of points representing different loop lengths.